OVERALL PROGRAM PROJECT SUMMARY The goal of this Program Project is the discovery, design, synthesis, optimization and validation of small molecule antagonists of the HIV-1 envelope (Env) trimer, combined with the definition of their molecular, virological and cellular mechanisms of action to identify potential preventive and therapeutic approaches to attack the HIV- 1/AIDS pandemic. The HIV-1 Env trimer is the only virus-specific protein on both the exposed surface of HIV-1 virions and on HIV-1 infected cells, and as such is a crucial first target for prevention and intervention of virus infection. Compounds that can bind with sufficient affinity, specificity and breadth to sequence-conserved and functional centers on Env should be able to inhibit, inactivate, and/or prematurely activate Env on the virus and on infected cells. In so doing, such compounds could block both cell infection and the formation of new infectious viruses, and prime infected cells for eradication. Major advancements have been made in our Program Project during the past 5 years to identify small molecule HIV-1 Env inhibitors that [1] allosterically or competitively block HIV-1 cell receptor interactions and cell infection; [2] irreversibly inactivate both the virus and virus-infected cells; and [3] sensitize cells to antibody-mediated immune responses. This progress opens up important opportunities to identify and explore the fundamental mechanisms of Env antagonism. Our progress going forward in developing small molecule inhibitors will be greatly facilitated by a deepening understanding of conformational states, dynamics and high-resolution structures of the HIV-1 Env trimer, as well as an understanding of how this molecular machine is activated to mediate fusion between viral and cellular membranes. In turn, the understanding of Env trimer structure and dynamics will be aided by small molecule inhibitors, developed by our Program Project, that function as chemical probes to inhibit, entrap or activate specific conformational states. The discovery, design, synthesis, optimization and validation of small molecules will enhance the identification of preventive, therapeutic and eradication interventions for HIV-1/AIDS. We will pursue a comprehensive mechanistic approach to investigate HIV-1 Env antagonism. To accomplish this, 7 investigators organized in 5 projects and 3 cores will pursue a multi-disciplinary integrated and synergistic approach. Knowing that no single group can succeed alone, the program has established a highly collaborative and efficient infrastructure, with an atmosphere where ideas are discussed early, new findings exchanged quickly, and the most effective strategies validated in order to fulfill the research goals. This Program Project will build both on an experienced group of investigators as well as the two new investigators to respond to new developments and challenges.